1. Field of the Invention
The present invention relates to a charging device, and more particularly to a charging device that charges a battery pack which can be mounted on an electronic device for supplying electric power to the electronic device.
2. Description of the Related Art
Recently, there is such a situation that electronic devices, such as digital cameras and cellular phones, can be purchased at low prices, and the number of users thereof increases. Accordingly, an increasing number of users own a plurality of charging devices for charging battery packs compatible with the respective associated electronic devices. This increases users who keep battery packs mounted on charging devices, and hence new charging devices have been proposed which are intended for prolonging the service life of the battery packs and saving of energy.
For example, for a method of charging a secondary battery using an output from a power supply circuit, there has been proposed a technique in which the voltage of the battery or the temperature of the battery is detected, and the operation of the power supply circuit is stopped when it is determined that the battery is fully charged, followed by terminating charging of the battery (see e.g. Japanese Patent Laid-Open Publication No. 2005-224016). In this technique, with a view to reduction of stand-by power of the charging device, there is provided a function (latching function) of completely stopping the ON/OFF operation of a switching element that controls supply of DC current to a primary control circuit of the charging device. Further, there is also proposed a method of terminating charging of the battery by a timer.
However, in the above-mentioned conventional technique disclosed in Japanese Patent Laid-Open Publication No. 2005-224016, since the latching function of completely stopping the ON/OFF operation of the switching element that controls supply of DC current to the primary control circuit of the charging device is used, it is required to pull out an AC plug of the charging device from an AC outlet, and then insert the AC plug again into the AC outlet. Further, the method of terminating a charging operation using a timer can cause overcharging of the battery though it can fully charge the battery.